Doppler flowmeters measure the velocity of sonic scattering material in a pipe or other conduit relative to the geometry of the sound source and sound receiver of the measuring system. A single crystal Doppler flowmeter is disclosed in U.S. Pat. No. 4,579,005 to A. Brown, assigned to the assignee herein. Other Doppler flowmeters for the same purpose involve two crystals, one for transmitting and one for receiving.
Typically, a continuous ultrasonic wave transmitter, known as a transducer, directs sound into a flowing medium containing particles or bubbles which reflect or scatter the sound back to a sonic receiver. The received sound has been shifted in frequency as a function of the moving scatterers. This can be expressed by the equation: ##EQU1## where: f.sub.d =Doppler frequency
v=velocity component of flow subtended by sonic beam PA1 c=speed of sound in medium PA1 f.sub.o =transmitted frequency PA1 f.sub.d '=simulated Doppler signal, and PA1 x=division rate of the multiplier.
It should be understood that v is a vector component of velocity of the scattering particles in the flowing medium in a direction relative to the transmitter.
Presently, to accurately test or calibrate a Doppler ultrasonic flowmeter, a pipe of known characteristics is needed having a known flow velocity for a specific fluid, such as water. Many times a person desiring to test a flow meter does not have such a pipe available and so an inaccurate test or calibration is performed.
Previously, circuits have been devised for Doppler flowmeters which simulate flow. Typically, a flow simulator is merely an audio oscillator which is not calibrated and not a good simulator.
An object of the invention is to devise an accurate universal Doppler flowmeter tester or calibration circuit which simulates liquid flow in a pipe.